Atrial Septal Defect
A 5-year-old boy is referred after a murmur was heard at a school health check. He is asymptomatic with normal growth. There is a grade 2/6 ejection systolic murmur at the upper left sternal border with a widely split second heart sound that does not vary with respiration. Electrocardiography shows an rSR pattern in lead V1 with right axis deviation. Which of the following is the most likely diagnosis?
- A.Patent ductus arteriosus
- B.Secundum atrial septal defectCorrect
- C.Ventricular septal defect
- D.Atrioventricular septal defect
Explanation
A fixed widely split second heart sound with a soft pulmonary flow murmur in an asymptomatic child, together with an incomplete right bundle branch block pattern (rSR in V1) and right axis deviation on the electrocardiogram, is the classic picture of a secundum atrial septal defect. The left to right shunt at atrial level produces chronic right ventricular volume overload, which delays right ventricular emptying and pulmonary valve closure equally in inspiration and expiration, hence the fixed splitting, and stretches the right ventricular outflow producing the rSR conduction pattern. The murmur is not from flow across the defect itself, which is low velocity, but from increased flow across the pulmonary valve, and a tricuspid mid diastolic rumble may also be heard when the shunt is large. A patent ductus arteriosus produces a continuous machinery murmur below the left clavicle with bounding pulses and a wide pulse pressure. A ventricular septal defect produces a harsh pansystolic murmur at the lower left sternal border with left ventricular volume overload and left axis deviation when large. An atrioventricular septal defect characteristically shows a superior (northwest) QRS axis and is strongly associated with Down syndrome. Other causes of right bundle branch block in children include chronic lung disease, cardiomyopathy, prior surgery for tetralogy of Fallot, and normal variation. Secundum defects that remain significant beyond early childhood are usually closed by transcatheter device to prevent later atrial arrhythmias, paradoxical embolism, and pulmonary vascular disease.
Why each option
- A.
- A patent ductus arteriosus gives a continuous machinery murmur with bounding pulses, not fixed splitting with right bundle branch block.
- B.
- Correct. Fixed splitting of the second heart sound with an rSR pattern in V1 indicates a secundum atrial septal defect.
- C.
- A ventricular septal defect causes a harsh pansystolic murmur at the lower left sternal border with left sided volume overload.
- D.
- An atrioventricular septal defect typically shows a superior QRS axis and is associated with Down syndrome.
Reference: Nelson Textbook of Pediatrics, 22nd ed., 2024, Atrial Septal Defect
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